DE-PS 22 37 884 and associated U.S. Pat. Nos. 4,001,357 and 4,060,355 disclose a rule for optimizing the geometrical form of a Laval supersonic nozzle arrangement in the flow direction as a function of the properties of the molten material. It must be stressed as an essential feature of this optimizing rule, which is intended for the production of fibres, that when the primary molten jet enters the expansion zone, i.e. after it passes through the narrowest cross-section at mach 1, and after formation of the bundle of fibres, consisting of several secondary molten fibers of .mu.m diameter, cooling and solidification in the expansion zone must take place very rapidly. In any case, this solidification occurs already prior to hydrodynamic instability, causing a collapse into tiny balls or droplets.
To optimize a supersonic propellent gas apparatus to produce superfine powder in diameters ranging from about 5 to 30 .mu.m from the molten materials mentioned at the outset, it is necessary, according to the rules of the procedure disclosed in U.S. Pat. No. 4,534,917, to keep the molten batch fluid by supplying heat to this area (instead of a rapid cooling of the bundle of secondary threads). This is accomplished most expediently by means of radiant heat.
An important condition is that the propellent medium flow should be kept laminar.
Therefore, the invention solved the problem by providing a method whereby the necessary supply of heat and the laminar flow pattern of the propellent medium is ensured, so as to guarantee the formation of superfine powder particles by preventing the formation of larger diameter drops.